The invention relates to a method and apparatus useful for the preparation of multiple gauge metal strip of exacting tolerance by a drawing operation employing hydrodynamic lubrication.
In many applications, such as the production of copper strip for the formation of electrical connectors and the like, it is necessary to provide a multiple gauge thickness in the metal strip. Heretofore, such conventional procedures as continuous milling and continuous shaving have been employed to produce the desired variations in gauge. Such processes suffer from the disadvantages of being both highly scrap intensive and in the case of milling time-consuming.
Another procedure which has been investigated in the art is the reduction to gauge by a rolling operation. Rolling operations in production are normally only accurate to about 10% and are not good enough to provide products meeting commercial tolerances that are free from structural defects such as camber, edge waves, buckling or longitudinal cracking. One method of rolling which has been successfully developed is disclosed by Applicants in copending application Ser. No. 439,519, entitled "METHOD FOR PRODUCING MULTIPLE GAUGE STRIP", now Pat. No. 3,866,451, and deals with a technique known as grooved rolling wherein strip reduction is confined to the area of contact with the grooves of the roll assembly.
In addition to the techniques outlined above, examination has been made of drawing techniques with appropriately configured dies. Generally, the preparation of a multiple gauge product by drawing results in complications caused by conventional metal flow. That is, in the normal drawing process, reduction of the thickness in a section results in an increase in section length, so that if the thickness of a given shape varies across its width, the drawing process will result in variable changes in length causing non-uniform metal flow and stresses leading to buckling, twisting, tearing and fracture of the workpiece. Though a wide variety of drawing techniques are known, including the employment of the hydrodynamic principle, none have been suggested or would appear to alleviate the aforenoted deficiencies associated with the drawing of complex multiple gauge configurations.